[python] Re: wheel flop vs pedaling induced steering

  • From: Rhisiart Gwilym <Rhisiart@xxxxxxxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Wed, 28 Nov 2007 20:08:50 +0000

On 28.11.2007 16:50, Kevin Bailey wrote:

 I had assumed that PSI was dependent on the ratio between the
 pedal "width" (distance from the center of the pedal to the
 centerline of the bike) and the BB to pivot distance. Basically,
 that PSI was caused by the sideways component of the pedaller's
 stroke (which attempts to turn the wheel) and corrected by the
 foward component of his stroke (which attempts to straighten the
 wheel.) This ratio is equivalent to that between the pedal width
 and the BB to pivot distance. Put plainly, the further back you
 move the pivot (without changing the pedal width), the less the
 PSI. I assumed this was why the Python was better in this
 respect than the Traylor/Cruzbike designs.


Hello Kevin,
I thought this too - until I built the PX.5, an experimental prototype where the pivot was moved 25 cm further back than the normal position: 

http://python-lowracer.de/pics/Python%20PX.5.jpg

PSI was clearly noticeable and the bike was hardly rideable.

Cheers,
Jürgen.


Siwmae Jurgen,
That picture seems to me like a very striking image of a man actually sitting on a unicycle, with the one-wheel trailer towed behind, rather than the rider sitting on the trailer to drive and steer the front-end/unicycle from behind, so to speak. Wonder if that has anything to do with PSI. It's certainly surprising that it comes back in that layout, and makes the bike hard to manage. Mysterious! 

Cof,  RhG
PS, 'pedal-steer interference' and 'pedal-induced steering' both sound natural -- though PIS is going to phase some English-speakers, perhaps. 
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